<html>
<body>

<select id="s">
    <option>Volvo</option>
    <option>Saab</option>
    <option>Mercedes</option>
    <option>Audi</option>
</select>

<button type="button" id="bt">Click Me!</button>
<script src="https://cdn.bootcss.com/jquery/3.3.1/jquery.min.js"></script>
<script>
    $("#bt").click(function () {
        alert($("#s").find("option:selected").text());
    })
</script>
</body>

</html>
